Management of Cleome rutidosperma DC. using high crop density in dry-seeded rice

Abstract

Cleome rutidosperma is one of the invasive C3 weed species in dry-seeded rice systems in South and Southeast Asia. Cleome species have shown a cytological developmental progression from C3 to C4 photosynthesis. Hence, a better understanding of growth responses of the weed in rice is critical in developing sustainable integrated management approaches for the suppression of this weed. Physiological and morphological changes of C. rutidosperma were studied in a pot experiment by growing the weed alone (1 plant per pot; 0.045 m2) and in competition with 4, 8, 12, and 16 plants per pot of two rice cultivars namely, IR64 and SACG4, in separate pots. The plant height of C. rutidosperma was not affected by the rice density or cultivar, and the height increased linearly with increasing time. The leaf area production of the lower half of the weed was reduced by 80–88% when grown with 12 and 16 rice plants compared to that grown without rice interference. Rice interference at the density of 16 plants per pot reduced leaf biomass of the weed by 92%, inflorescence biomass by 93%, stems biomass by 90%, and root biomass by 92% compared to the weed plants grown alone. The leaf and stem biomass allocation was higher to the lower half of the weed than that to the upper half, when grown in competition with rice. The specific stem length of C. rutidosperma increased by 84% in the presence of 12 rice plants (sowing density 60 kg/ha) compared to 4 plants (sowing density 20 kg/ha), indicating the change in resource allocation to stem elongation to enable the weed to compete effectively under shade to acquire light. However, the relative growth rate of the weed declined by 28% and 54% in the presence of 16 rice plants (sowing density of 80 kg/ha) during 3–5 and 5–7 weeks after sowing, respectively, compared to when the weed was grown without rice interference, reflecting less competitiveness of the weed for the resource acquisition under crop competition. The results of this study showed that the rice interference alone can reduce the weed's growth to a great extent. Therefore, the need of integration of other management practices in dry-seeded rice along with crop interference is highlighted to achieve complete control of C. rutidosperma and similar weeds.